1. Field of the Invention
This invention relates to hydraulic ram type actuators. More particularly, it relates to the provision of a hydraulic ram type actuator system which is capable of accepting a digital command and which exhibits certain advantages in efficient use of hydraulic power and an invulnerability to hardover failure of its output element when compared with a valved ram or a valved rotary hydraulic motor driven servo.
2. Description of the Prior Art
The actuator system of this invention is suitable for, but not limited to, use for positioning control surfaces of an aircraft, e.g. a flap.
Conventional systems for positioning control surfaces of an aircraft normally utilize a valved ram or valved rotary hydraulic motor type actuator. A disadvantage of these systems is that the valved hydraulic ram or motor cannot adapt its power consumption to load demands and must dissipate large amounts of hydraulic power across the orifices of its control valve whenever a high rate with less than maximum output force or torque is demanded. A second disadvantage of such systems is that they require a feedback to insure adequate dynamic response and as a result are susceptible to a hardover reaction of the output in the event of a loss of the feedback signal continuity.
There are some flight control surface actuators in existence which have power conserving properties when used on dynamically active surfaces. However, under static output conditions, these systems waste power by keeping a variable displacement pump in constant rotation at a high rotational speed.
Present trends of aircraft actuation systems are toward electrically controlled hydraulic actuators. Centrally located on-board digital computers or dispersed individual microprocessors are foreseen to provide the command signals to these actuators. Present state-of-the-art actuators and controls are analog type devices that require digital to analog conversion components to be compatible with the digital electric control signals.